Research and development of a microchip for analyzing a sample of an organism substance or the like by fabricating a channel of a micrometer size or a channel which is a reaction tank on a chip have energetically been carried out over 20 years, and practical application is being progressed. There are a number of cases where a member of a microchip is configured by a transparent glass or resin, an outer dimension thereof variously ranges from several mm through several tens cm, and a thickness thereof is smaller than the size described above. A small amount of a sample can be analyzed simply and conveniently in a short time on the spot by a microchip. As examples of microchips which have already been put into practice, there are PCR, real time PCR, digital PCR, electrophoresis analysis, immunity analysis (immunoassay), flow cytometer (cell sorter), single cell analysis, microreactor, and so on. A microchip integrated with steps of analysis including introduction, extraction, mixing with a reagent, and reaction of a sample is referred to as a micro TAS (Total Analysis System) or Lab on a Chip, and research and development for resolving various problems toward practical application is successively and intensively carried out. As measuring means of a microchip, there are a number of cases where light measurement which can measure a substance present at an inner portion of the channel in noncontact. For example, a fluorescent substance is labeled on an organism substance in a channel, an unlabeled fluorescent substance is removed, then, fluorescence emitted by irradiating a laser beam is measured. Or an organism substance is observed by an optical microscope, and the shape or the number thereof is measured, and so on.
A microchip made of resin can be fabricated by a fabrication technology of injection molding, nanoimprinting or the like, and can be mass-produced at low cost, and therefore, the microchip is also disposable. Such a disposable microchip is particularly important in a field in which it is strongly requested to avoid contamination other than a sample to be analyzed such as medical diagnosis, food inspection or the like. It is important to configure a number of channels on a single chip, and measure the channels in parallel in a case where a number of items are analyzed in parallel concerning a single example, in a case where plural kinds of samples are measured in parallel, and in view of reducing cost per single analysis by improving a throughput of measurement thereby. Or a time-sequential change of a reaction or a separation can be analyzed by measuring plural portions of a single channel in parallel.
Here, it is a big problem how efficiently a laser beam is irradiated to plural channels provided on a microchip to thereby carry out an analysis by fluorescence measurement, scattered light measurement, transmitted light measurement or the like, and conventional methods are classified to following (1) through (5). A description will be given by taking an example or fluorescence measurement as follows. In any of the methods, laser beam irradiating portions of plural channels are arranged in parallel on the same plane in a chip. Hereinafter, the plane is referred to as an array plane. In a case where plural portions of a single channel are measured in parallel, portions of the channel which are intended to measure are arranged in parallel on the same plane in a chip by turning back the channel by plural times.    (1) Bean enlarging system: enlarging a laser beam to spread over plural channels to simultaneously irradiate and simultaneous detecting of fluorescence from the plural channels
There are a case of enlarging a laser beam in a shape of a line and simultaneously irradiating plural channels and a case of enlarging a laser beam in a circular shape or an elliptical shape and simultaneously irradiating plural channels. In comparison with a case of irradiating a laser beam by focusing the laser beam to a single channel, in a case of simultaneously irradiating N channels, a laser beam intensity per single channel is reduced to (1/N) or less when enlarged in the shape of the line, and to (1/N2) or less when enlarged in the shape of the circle. Therefore, fluorescence detection sensitivity of each channel is reduced. Although there is also conceivable a case of dividing a laser beam into plural pieces thereof and irradiating the respective laser beams to respective channels as one mode of the beam enlarging system, a problem similar to the above-described is posed.    (2) Beam scan system: when a system of focusing a laser beam to irradiate to a single channel and detecting fluorescence from the same channel is scanned with respect to plural channels
When compared with a case where a laser beam is focused to a single channel and is not scanned, in a case of irradiating N channels serially by scanning, effective density of a laser beam intensity per single channel is reduced to (1/N) or less, and fluorescence detection sensitivity of each channel is reduced. Further, also a time resolution of each channel is reduced to (1/N) or less, which maybe disadvantageous in view of measurement. Further, a scanning mechanism is needed, and therefore, there is also a drawback that a device is large-sized, and requires high cost, and a failure is increased.    (3) Independent beam irradiation and detection system: systems of focusing a laser beam to irradiate a single channel, and detecting fluorescence from the same channel are installed by as many as plural channels
Although when an optimum laser or an optimum detector can be used for each channel, high fluorescence detection sensitivity can be obtained for any channel, in this case, cost of the device is very high. On the other hand, plural channels which can be laid out on the same chip are obliged to be proximate to each other, and therefore, it is physically difficult to provide a highly sensitive laser irradiation fluorescence detection system for each channel. Therefore, it is necessary to adopt a small-sized laser irradiation fluorescence detection system at low cost in which sensitivity is not comparatively high.    (4) Beam waveguide system: irradiation of plural channels by an evanescent wave bypassing a laser beam to a light waveguide contiguous to plural channels, and simultaneous detection of fluorescence from plural channels
A laser beam irradiation volume can be made to be very small by an evanescent wave, and therefore, the system is advantageous in a case where fluorescence originated from, for example, a single fluorescence molecule is detected highly sensitively by reducing background light originated from a solution in the channel. However, in many cases, an object substance detected by a microchip is not such a small number molecule but a large number molecule. In such a case, when a laser beam irradiation volume is excessively reduced, sensitivity is reduced.    (5) Beam side-entry system: irradiation of a laser beam to traverse plural channels vertically to long axes of respective channels along an array plane from a side face of a chip, and simultaneous detection of fluorescence from plural channels from a direction vertical to the array plane
Although the highest sensitivity can be expected by the simplest and the most convenient configuration, a laser beam is refracted at an interface of each channel, and therefore, it is difficult to efficiently irradiate plural channels. Center positions of respective channels subjected to laser beam irradiation are arranged on the same linear line by the beam side-entry system. Hereinafter, the linear line is referred to as a beam side-entry axis. The beam side-entry axis is disposed on the array plane, and is vertical to long axes of respective channels. Here, the long axes of the respective channels are linear lines or curves passing centers in longitudinal directions of respective channels or gravitational centers of sections. In Patent Literature 1, a laser beam is irradiated by aligning the laser beam with the beam side-entry axis, and plural channels can be penetrated without deviating from beam side-entry axis by condensing a laser beam refracted by respective channels by inserting lenses or mirrors among the channels, and highly sensitive fluorescence detection can be carried out. On the other hand, in Nonpatent Literature 1, a laser beam is aligned with abeam side-entry axis, the irradiation is carried out by enlarging a width of the laser beam more than a channel width, and plural channels are simultaneously irradiated. In a case of irradiating by enlarging a laser beam width more than a channel width, a laser beam intensity density is reduced and fluorescence detection sensitivity is reduced.